FIGS. 1A and 1B show respective perspective and diagrammatic side views of a prior art overhead projection display panel 10 that operates with a conventional overhead projector light source 12 to display computer-generated information on a projection screen 14. Overhead projector 12 includes a projection lens assembly 16 that projects onto projection screen 14 light received from a light surface 18. The light transmitted from light surface 18 passes through an information-bearing medium, such as a sheet of transparent film or display panel 10, and carries the information to projection screen 14.
Display panel 10 selectively activates pixels within a transmissive liquid crystal device 20 to attenuate light received from light surface 18 of overhead projector 12 according to display data received from a personal computer (not shown) or other video source. As a result, display panel 10 modifies the light generated by overhead projector 12 to form the computer-generated image on projection screen 14. Such a display panel is described in U.S. Pat. No. 4,917,465 of Conner et al., issued Apr. 17, 1990 and assigned to the assignee of the present application.
Display panel 10 includes a substantially rigid annular case 26 with side margins 28a-28d that support liquid crystal device 20 within an aperture 30. Case 26 encases electronics 32 (shown in outline), which control liquid crystal device 20, within at least one of side margins 28a-28d and supports a control panel 34 that controls various display characteristics of the display panel such as, for example, color, contrast, cursor position, or switching to different display images. Case 26 is of a relatively large size with a length 36a and a width 36b that are greater than the corresponding 10 inch (25 cm) length 38 and width (not shown) of light surface 18. The relatively large size of case 26 allows it to perform three functions: support liquid crystal device 20 over light surface 18, encase the electronics that control liquid crystal device 20, and occlude light emitted from portions of light surface 18 not aligned with liquid crystal device 20. The occluding function allows display panel 10 to form the computer-generated display images without distracting extraneous boundaries of unused light.
A consequence of the relatively large size of case 26 is that display panel 10 is relatively bulky and cumbersome to handle or store (i.e., lacks portability), particularly when compared to modern laptop personal computers. Moreover, to prevent the size of case 26 from being even greater, the electronics for controlling or powering liquid crystal device 20 often do not include all possible features.